Broadband microwave attenuation measurement standard in the frequency range from 10 MHz to 26.5 GHz

A broadband microwave attenuation measurement standard using audio frequency substitution method is described in this paper. The broadband standard includes a single channel and a dual channel system. The single channel system is used to perform accurate attenuation measurement from 10 MHz to 2 GHz. From 2 GHz to 26.5 GHz, the dual channel system is used to reduce the receiver noise and improve the measurement accuracy. Attenuation up to 110 dB can be measured by this standard. The measurement uncertainty of the standard is also analyzed. The expanded measurement uncertainties of a 0.01 dB ~ 110 dB variable attenuator are estimated to be 0.0028 dB ~ 0.028 dB from 10 MHz to 26.5 GHz.

I Introduction

Audio frequency (AF) substitution systems have been used by some national standard laboratories as microwave attenuation measurement standards [1]–[10]. In such systems, the microwave signal is converted to AF signal (1 kHz to 50 kHz) using a mixer, and the microwave attenuation is derived from the voltage ratio at AF. An Inductive Voltage Divider (IVD) is usually used as a traceable low frequency voltage ratio reference standard for the microwave attenuation measurement. In [2], an AF series substitution system was described which used a phase sensitive detector to make accurate attenuation measurement from 0.5 MHz to 100 MHz. An AF series substitution system was also developed which employed a reference channel and null detection method for accurate attenuation measurement [3]–[4]. In this system, an optical fiber link is used to reduce the internal RF leakage introduced by the reference channel. The system can measure attenuation up to 100 dB from 10 MHz ~ 12 GHz and up to 60 dB from 12 GHz ~ 18 GHz [4].